[Driver] Make scudo compatible with -fsanitize-minimal-runtime

Summary:
This is the clang side of the change, there is a compiler-rt counterpart.

Scudo works with UBSan using `-fsanitize=scudo,integer` for example, and to do
so it embeds UBSan runtime. This makes it not compatible with the UBSan minimal
runtime, but this is something we want for production purposes.

The idea is to have a Scudo minimal runtime on the compiler-rt side that will
not embed UBSan. This is basically the runtime that is currently in use for
Fuchsia, without coverage, stacktraces or symbolization. With this, Scudo
becomes compatible with `-fsanitize-minimal-runtime`.

If this approach is suitable, I'll add the tests as well, otherwise I am open
to other options.

Reviewers: eugenis

Reviewed By: eugenis

Subscribers: llvm-commits, cfe-commits

Differential Revision: https://reviews.llvm.org/D48373

llvm-svn: 335352